ISCHEMIA INDUCED NEUROGENESIS AND PLASTICITY

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DESCRIPTION (From Abstract): New cells are born in the brain throughout adult life. One source of newborn cells is the subgranular zone of the dentate gyrus of the hippocampus. The newborn cells have the potential for forming neurons, astrocytes or oligodendrocytes. Many cells born in the subgranular zone that migrate into the granule cell layer form mature neurons. NMDA receptors, seizures and stress hormones regulate this neurogenesis. We have found that ischemia also up-regulates neurogenesis. BrdU immunohistochemistry was used to show a 9-fold increase of cell birth in the dentate subgranular zone 1-2 weeks following global ischemia. The newborn cells in the subgranular zone migrate into the granule cell layer where 60-66% mature into neurons. Some of the cells born in the subgranular zone also migrate into the dentate hilus where 10-20% become astrocytes. The ischemia-induced dentate neurogenesis was not caused by stress of by cell death in entorhinal cortex. The present study is designed to examine the fate of the newborn neurons and to examine the mechanism of ischemic induction of neurogenesis in the rodent brain. It is hypothesized that the neurons born in the dentate following global ischemia: extend axons to the target CA3 pyramidal neurons; up-regulate synaptic proteins; increase the numbers of synapses on CA3 pyramidal neurons; and increase the total number of neurons in the dentate granule cell layer. Experiments will determine: whether retrogradely transported dyes injected into the CA3 zone of hippocampus co-localize with BrdU labeled nuclei and the NeuN, MAP-2 and calbindin neuronal markers in the dentate granule cell layer following global ischemia; Whether pre-synaptic proteins are up-regulated following global ischemia in the newborn neurons and in the CA3 zone of hippocampus; whether the number of mossy fiber synapses on CA3 pyramidal neurons increases following ischemia; and whether the total number of granule cell neurons changes following global ischemia. It is also hypothesized that erythropoetin is induced in glial cells in the ischemic hippocampus, is released and acts on erythropoetin receptors on dentate progenitor cells to initiate proliferation of the progenitor cells and increased neurogenesis. Experiments will determine whether: erythropoetin and/or erythropoetin receptors are increased in hippocampus following global ischemia; whether ventricular infusion of erythropoetin increases neurogenesis from dentate progenitor cells; and whether ventricular infusion of antibodies to erythropoetin and/or erythropoetin receptors attenuate neurogenesis following global ischemia. These studies are important for understanding the mechanism of recovery of function following ischemic injury to the hippocampus.